This application claims the benefit of Korean Application No. 00-37391, filed Jun. 30, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical pickup assembly having efficient acceleration capability at a voltage level and suitable for high-speed and high-density optical recording/reproduction systems.
2. Description of the Related Art
Optical pickup assemblies are adopted in optical recording/reproduction systems so as to record information on and reproduce information from a recording medium, i.e., an optical disc, seated on a turntable. Here, the optical pickup assemblies move in the radial direction of the optical disc and are not in contact with the optical disc. As shown in FIG. 1, a conventional optical pickup assembly includes an actuator for driving an objective lens 1 in the track and focus directions of an optical disc (not shown) so as to form a light spot on a target track of the optical disc. The actuator includes a base 10, a bobbin 13 on which the objective lens 1 is mounted and which is installed on the base 10 such that it is movable, a suspension 17 in which one end is fixed to the bobbin 13 to support the bobbin 13, such that the bobbin 13 is movable relative to the base 10, and in which the other end is fixed to a holder 15, a focusing coil 21 and a tracking coil 23 wound around the bobbin 13, inner and outer yokes 25 and 27 formed on the base 10, and permanent magnets 29 attached to the inner sides of the outer yokes 27, such that they face the tracking coil 23.
The bobbin 13, which is formed of plastic by molding, supports the objective lens 1. The bobbin 13 acts as a guide in the winding of the focusing coil 21 and the tracking coil 23, and has through holes 13a for receiving the inner yokes 25. The objective lens 1 is seated on the top of the bobbin 13, and the focusing coil 21 and the tracking coil 23 are wound around the sides of the bobbin 13 in a bulk type fashion, such that the objective lens 1 is driven in the focus and track directions of the optical disc as a current applied to the focusing coil 21 and the tracking coil 23 interacts with magnetic flux generated by the permanent magnet 29.
The bobbin 13, the objective lens 1, the focusing coil 21 and the tracking coil 23, which are mounted on the bobbin 13, collectively constitute a moving part of the optical pickup assembly. In the conventional optical pickup assembly having the above configuration, the bobbin 13 accounts for about 50% of the total weight of the moving part. Due to the heavy weight of the moving part, it is difficult for the conventional optical pickup to be driven with high sensitivity.
The xe2x80x9csensitivityxe2x80x9d is a measure of the capability of a moving part to accelerate with application of a voltage, and is expressed in units of g/V, where g represents the gravitational acceleration of 9.8 m/s2, and V represents voltage in volts. The acceleration of the moving part including the objective lens required for tracking at a given voltage is determined based on the sensitivity. The degree of sensitivity is proportional to the effective magnetic flux density and the effective coil length, and inversely proportional to the weight of the moving part.
The configuration of the bobbin 13 having the through hole 13a and the weight of the moving part increase moment of inertia, and thus the secondary resonance frequency of the driving part becomes low due to a higher order resonance mode of the bobbin 13 itself. As a result, the frequency bandwidth for servo control is limited. Thus, there is a limitation in improving the sensitivity in driving of the driving part with respect to actuation, so that the conventional optical pickup cannot be applied to a high-speed and high-density optical recording/reproducing system. Furthermore, an additional step of mounting the objective lens 1 on the bobbin 13 is needed, so that a failure occurs due to assembling errors. In addition, the manufacturing cost increases due to increased man-hours for assembling.
Accordingly, it is an object of the present invention to provide an optical pickup assembly suitable for high-speed and high-density optical recording and reproduction systems, which adopts a lightweight moving part so that it can be efficiently actuated at a voltage level, and in which the secondary resonance frequency of the moving part can be increased.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing objects of the present invention are achieved by providing an optical pickup assembly comprising: a base; an objective lens including a body portion, and a lens portion built into the body portion; a suspension whose one end is fixed to the body portion and whose other end is fixed to a holder supporting the objective lens such that the objective lens is movable; a coil member formed at the sides of the body portion of the objective lens; permanent magnets mounted on the base, opposite to the coil member; and yokes guiding magnetic flux generated by the permanent magnets.
According to an aspect of the present invention, the objective lens, the suspension and the holder are formed as a single unit by injection molding. The lens portion and the body portion of the objective lens may be formed of the same material.
According to an aspect of the present invention, the coil member includes a focusing coil and a tracking coil, and is patterned as a planar printed circuit board type. Alternatively, the coil member can be directly patterned into the sides of the body portion of the objective lens by etching and/or deposition processes.
It is preferable that the yokes are outer yokes, the permanent magnets are attached to the inner walls of the outer yokes, and the yokes are mounted on the base.